Punching metal bars, plates, and the like



Feb. 2 0, 1945.

PUNCHING METAL BARS, PLATES, AND THE LIKE s. c.' HARRIS ET AL Filed July 16, 1943 D APPROXIMATELY 2% OFT Patented Feb. 20, 1945 PUNCHIN G METAL BARS, PLATES, AND

- THE LIKE Samuel C. Harris and Edwin B. Greifenhagen,

Milwaukee, Wis., assignors to Chain Belt Com-' pany, Milwaukee, Wis., a corporation of Wiscousin Application July 16, 1943, Serial No. 494,975

9 Claims.

The invention relates to the punching of metal bars, plates and the like, and has for its principal object the facilitation of the production of punched holes in such objects which will compare favorably with drilled and reamed holes as regards finish, accuracy of size, and lack of taper.

Under the practice heretofore commonly employed in the metal working industry, accurately sized, parallel-sided punched holes in bars and plates having a thickness of inch and upwards are secured as a result of two separate operations. The first of these consists in subjecting the plate or bar to the action of a punch size and/or a high finish on the hole surfaces were desired, the practice has been to ream the holes.

The double operation just described has of course consumed time and added to costs, and the industry has long appreciated the desirability of being able to produce by a single operation a punched hole in metal plates and bars which would compare favorably enough with a drilled and reamed hole as to size, lack of taper,

- and finish to be practical. The present invenand die in a punch press whereby a rough hole is produced, and since the pressure necessary to force the punch through the metal is a function of the clearance between the punch and the die hole, the practice has been to provide clearance between thepunch and die equal to approximately 10% of the thickness of the plate or bar being punched. Clearances of this order have been found to materially reduce breakage of the, punches, both in the forcing of the punch through the metal and in the stripping" or withdrawal of the punch from the metal after it as been forced therethrough.

The diameter of the hole in the die is ordinarily equal to that of the hole desired in the metal, while the diameter of the punch is such as to give the 10% clearance referred to above. and this results in the rough hole being tapered. having a diameter equal to that of'the punch at one end and a diameter equal to that of the die hole at the other. The surface of the hole wall is also relatively rough; and the existence of these conditions has made necessary the second operation above mentioned where accurately absolutely essential, this second operation has consisted in subjecting the bar or plate to a second punching action in which a punch having a diameter providing a clearance of approximately .007 of an inch between it and the die hole-the diameter of which was the same as in the first operation-was forced through the rough hole. The action of this second punch was to broach or shave ofi the metal at the smaller end of the rough hole to within approximately of an inch of the larger end, thereby producing a substantially parallel-sided hole of approximately the desired size. The surface of the hole wall, while smoother than that of the rough hole, was not comparable to that of a reamed hole, and where absolute accuracy as to tion has been thoroughly tested in the punching of holes in iron and steel bars to be used as the side bars of power transmitting sprocket chains, and has been found to fully meet the relatively exacting requirements of such art.v

The invention will be the better understood by reference to the accompanying drawing forming a part of this specification, in which like reference characters designate like parts in all the views, and in which- Figure 1 is a side elevational view of a punch constructed in accordance with the invention, showing it in preliminary relation to a die and a plate to be punched;

Figure 2 is an enlarged fragmentary vertical sectional view, illustrating the initial action of the punch shown in Fig. 1; and

Figure 3 is a view similar to Fig. 2, illustrating the subsequent action of the punch.

Referring more particularly to Fig. 1 of the said drawing, the stem ill of the punch is of a diameter D equal to that desired in the hole to be punched in the bar or plate ll, while the hole I! in the die l3 has a diameter equal to D plus approximately 2% of the thickness T of the plate H. For a longitudinal distance equal to approximately $4; of the thickness T of the plate, the diameter of the punch stem I ll is reduced by approximately 8% of the plate thickness T, as indicated at H, and thisreduced end portion is joined to the body of the stem by a straighttaper section IS, the length of which is approximately A; of the plate thickness T. The bottom face of the punch is preferably curved or hollowed out as indicated at I6 toproduce an annular shearing or cutting edge I! at the periphery, as best shown in Figs. 2 and 3.

The action of the punch 'and die just described is graphically indicated in said Figs. 2' and 3. As the punch descends the cutting edge l! of the reduced end portion I4 engages and shears through the upper surface of the plate II and the forcin out of the plug I8 is begun, as shown in Fig. 2. Since the diameter of the end portion I4 is less than the diameter of the die hole l2 by approximately 10% of the plate thickness T, the punching action is accomplished in accordance with the widely used clearance standards of the prior practice, and tends to produce a tapering hole 20. However, when the punch section M has penetrated the plate to a distance equal to about one third of the plate thickness, the straight-taper section l begins to engage the upper smaller-diameter portion of the hole being formed, and during th remainder of the working stroke of the punch said taper section produces a cold-flow of those portions 21 of the metal from the smaller end of the hole toward the larger end so that when the punch has reached the position shown in Fig. 3 it will have produced in a single operation an accurately sized, parallel sided hole of the desired diameter. Furthermore, due to the action of the taper section I 5 and the following portion of the body in of the punch the. surface of the hole wall will be found, upon withdrawal of the punch, to be quitesmooth or burnished; and in fact the hole will be found to compare favorably, for most practical purposes with a drilled and reamed hole as regards size, lack of taper, and finish.

The body In of the punch may be forced completely through the plate or bar H, but as this may produce a slight burr around the lower edge of the hole, it is preferred to stop the punch stroke with the meeting plane 22 of the body In and taper section IS a few thousandths of an inch short of the lower surface of the plate II, as indicated in Fig. 3. This is found to eliminate such burr, and in fact results in the equivalent of a slight bevel or breaking of the corner of the lower edge of the hole.

While one specific embodiment of the invention has been illustrated and described for purposes of disclosure, it will be obvious that those skilled in the art may vary the details without departing from the spirit of the invention, and therefore it is not wished to be limited to the above description except as may be required by the claims.

What is claimed is:

1. In apparatus for punching metal plates, bars and the like to produce in a single operation an accurately sized, parallel-sided hole: a die having an aperture; and a punch having a stem receivable in said die aperture and provided at its operative end with a portion of reduced transverse dimensions co-operable with said die aperture to produce a slightly flaring hole in the work Piece, said punch also having a section adjacent its said reduced end portion for flowing the metal of the wall of such hole longitudinally thereof from the smaller end toward the larger end thereof without separation of such metal from the work piece to bring the sides of the hole into substantial parallelism.

2. In apparatus for punching metal plates, bars and the like to produce in a single operation an accurately sized, parallel-sided hole: a die having an aperture; and a punch having a stem receivable in said dieaperture and provided with an operative end portion of reduced transverse dimensions co-cperable with the die aperture to produce a slightly flaring hple in the work piece, said punch also having a taper section joining the reduced end portion and the body of the stern for cold-flowing the metlal of the wall of such hole longitudinally from the smaller end toward the larger end thereof without separation of such metalfrom the work piece.

3. In apparatus for punching metal plates, bars and the like, to produce in a single operation an accurately sized, parallel-sided hole: a die having an aperture; and a punch having a stem receivable in said die aperture and provided with an operative end portion, ofreduced transverse dimensions and of a length less than the thickness of the work piece, co-operable with the die aperture to produce a slightly flaring hole in the work piece, said punch also having a section adjoining said reduced end portion for cold-flowing the metal of the wall of such hole longitudinally from the smaller end toward the larger end thereof simultaneously with the formation of the hole and without separation of such metal from the work piece. I

4. In apparatus for cold-punching metal plates.

bars and the like to produce in a single operation an accurately sized, parallel-sided hole: a die having an aperture; and a punch having a stem receivable in said die aperture and provided with an operative end portion, of reduced transverse dimensions and of a length equal to approximately one-third of the thickness of the work piece, co-operable with the die apertureto produce a slightly flaring hole in the work piece, said bars and the like to produce in a single operation an accurately sized, parallel-sided hole having a relatively highly finished wall surface: a die provided with an aperture having a transverse dimension substantially equal to the desired transverse dimension of the hole plus approximately 2 per cent of the thickness of the work piece; and a punch having a stem having a transverse dimension equal to that desired in the hole, said stem being provided with a reduced operative end portion having a transverse dimension substantially equal to that desired in the hole minus approximately 8' per cent of the thickness of the work piece, whereby said reduced end portion and die aperture may co-operate to produce a slightly flaring hole in the work piece, said punch also having a tapering section intermediate said reduced end portion and the body of the stem for cold-flowing the metal of the wall of such hole from the smaller end toward the larger end thereof.

6. Apparatus according to claim 5, wherein the length of the reduced end portion of the punch is less than the thickness of the work piece.

'7. Apparatus according to claim 5, wherein the length of the reduced end portion of the punch is approximately equal to one third of the thickness of the work piece, and the length of said tapering section is approximately equal t one sixth of such thickness.

8. In the cold-punching of metal bars, plates and the like, the method of producing an ac curately sized, parallel-sided hole in a single operation, which comprises forming a, slightly ta- 9. In the punching of metal bars, plates and the like, the method of producing in a single operatlon, an accurately sized, parallel-sided hole having a relatively highly finished wallsurface, which comprises forming a tapering hole through the work piece having a diameter at its smaller endsubstantially equal to the desired diameter minus approximately 8 per cent of the thickness of the piece, and a diameter at its larger end substantially equal to the desired diameter plus approximately 2 percent of the thickness of the piece; ,and simultaneously with at least a portion of the formation of such hole, cold-flowing portions of the metal of its walls from the smaller end of the hole toward its larger end to produce a burnished parallel side wall having the desired diameter.

SAMUEL C. HARRIS.

EDWIN B. GREIFENHAGEN. 

